As one of the most anticipated features to date, guesting will finally be implemented in just under two weeks on January 28th. Since launch, in order to play people who were currently on another home server, players had to take advantage of map overflows or dungeon instances that shared the same region. Now that restriction is being lifted and players are now able to be a guest on another world. Specifically, two worlds every 24 hours.
However, there is something to remember here. Much like the regional restrictions that currently prevent NA and EU servers from playing through dungeons together, guesting will only allow accounts of the same region to guest to each other. To quote Martin Kerstein,
"Because (different from a world transfer) we are not moving your character between data centers, you may only guest on worlds in the same region as your home world. Players on North American home worlds cannot guest on European worlds or vice versa."
With guesting comes the end of free server transfers. After the guesting update, transfers will require a tiered gem fee based on the current population of the desired server. Less populated servers will be less expensive to transfer to than a high population server. Transfers are still limited to once every seven days.
Remember! This update happens January 28th! If you are a chronic world-switcher, make sure you're snug tight in your home server before it lands to prevent getting stuck.